The present invention relates to scanning systems and methods for examining surfaces of bodies subject to wear or change over time. The invention has particular, although not exclusive, utility for measuring surfaces and comparing them against historical data to determine whether the surface needs repair or replacement.
Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Furthermore, throughout the specification, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
In many applications, it is necessary to assess the wear or change of a surface relative to a base or reference. This information can be utilised for various applications, including assessing whether a surface is safe for use, or when a surface requires repair or maintenance as a result of either wear or accumulation of deposits over time.
In certain applications, a liner is often employed as a cost effective means of protecting a base surface from wear or damage. Consequently, the liner takes up wear in preference to the base surface, and is replaced from time to time in lieu of replacing the base surface, which may be more difficult or more expensive to replace.
Assessing the degree of change of a surface, be it with or without a liner, is difficult and/or time consuming in certain environments, such as where the surface is disposed internally within a cavity or compartment of a body, and especially where that body is rotatable. Conventional measurement tools are often inadequate to perform the task, either with respect to the precision of measurement, safety of performing the task, or economic factors associated with downtime of commercial use of the body whilst the measurement task is undertaken.
In some of these environments liners are used. It is important that liner wear is accurately determined to first ensure the liner is replaced before it wears to a point where it no longer protects the underlying body, and second to maintain the efficiency of the process.
A practical example of the foregoing considerations is in the comminution of minerals within the mining industry. In mineral processing, minerals are extracted from their interlocked state in solid rock by crushing the raw ore into progressively smaller pieces and finally grinding it into a powder. This comminution process is multi-stage, being carried out in a series of crushing then grinding mills, and generally includes transfer chutes to transfer the bulk material.
On the completion of the crushing process, the crushed ore is separated into pieces of a few cm in diameter (actual size depends on the ore type) and may then be fed into rotating cylindrical mills. The rotation of a mill about its axis causes the ore pieces to tumble under gravity, thus grinding the ore into decreasingly smaller fractions. Some types of grinding mills are fitted with grinding bodies such as iron or steel balls (ball mills), steel rods (rod mills) or flint pebbles (pebble mills) which assist in the grinding process. Two specific types of mill are the autogenous mill (AG mill), which operates without any grinding body, and the semi-autogenous mill (SAG mill), in which a small percentage (usually around 10%) of grinding bodies (often steel balls) are added.
A typical mill grinding circuit will comprise a primary grinding system, consisting of a SAG or AG mill and into which the crushed raw ore is fed, and a secondary grinding system, consisting of ball, rod or pebble mills and into which the output from the primary grinding system is fed.
All types of cylindrical mills consist of a cylindrical shell with a feed arrangement at one end and a discharge arrangement on the other. Feed and discharge designs vary. For example, feed chutes and spout feeders are common, whilst screw-type, vibrating drum and scoop-type feeders are also in use. Discharge arrangements are usually classified as overflow, peripheral, grate and open-ended.
The interior of a cylindrical mill is surfaced with a lining designed for the specific conditions of mill operation. Liners can be made of steel, iron, rubber, rubber-steel composites or ceramics. Liners in this application serve two functions:                1. to protect the shell of the mill from damage due to abrasion erosion;        2. to aid grinding performance.        
Naturally, mill liners wear through erosion. Normally, chemical solutions that are quite toxic and corrosive to humans and instrumentation alike are introduced into the mill to help with the comminution process. Whilst good liner design can enhance milling efficiency, worn liners have a detrimental effect on milling performance and energy efficiency. Therefore liners must be replaced on a regular basis.
Replacing mill liners requires significant mill downtime which is undesirable from an economic point of view. The downtime is attributable to the time taken to assess the thickness of the liner, and the considerable time needed to replace the liner. Therefore, accurately assessing the thickness of the liner within the mill is of critical importance to the operator. Furthermore, the minimisation of downtime attributable to liner thickness inspection procedures is also desirable.
Taking mills as an example, one method that has been used to determine liner thickness is visual inspection. Once the mill has been stopped and decontaminated, a specialist enters the mill and inspects the liner for cracks, fractures and excessive wear. The problem with this approach is the time consumed in decontaminating the mill, and further, the inaccuracy of relying on the human eye to determine the thickness of an object of which the depth dimension is invisible.
Another method of determining mill liner thickness is via a physical inspection. As is the case with visual inspection, the mill must be stopped and decontaminated before the mill is inspected. A specialist enters the mill and measures the length of nails that have previously been hammered into the liner. As the liner wears faster than the protruding nail, inspection of the length of protrusion provides an indication of wear. The problem with this method is that it is time consuming in terms of mill downtime while decontamination procedures and measurement processes are executed, and further, the inaccuracy of estimating the thickness from measurements of the nail, which itself is subject to wear, against the liner wear. Further, the comparative sparsity of measurement coverage of the liner is also a problem.
Another method of determining mill liner thickness is via acoustic emission monitoring. This method involves monitoring the surface vibrations on the outside of a mill via accelerometer transducers. Estimates are obtained relating to grinding process performance and machine wear analysis. The problem with this approach is that it does not directly measure the mill liner thickness. Rather, it monitors changes in the acoustic output of a mill which could be interpreted as being due to mill liner wear, but could equally be attributable to wear of other parts of the milling machinery.
Another method of determining mill liner thickness is via ultrasonic thickness gauging. It is known by some in the industry to be a well-established technique typically performed using piezoelectric transducers. Ultrasonic gauges measure the time interval that corresponds to the passage of a very high frequency sound pulse through a test material. Sound waves generated by a transducer are coupled into the test material and reflected back from the opposite side. The gauge measures the time interval between a reference pulse and the returning echo. The velocity of sound in the test material is an essential part of the computation. The readings are obtained using a hand-held device which is operated manually within a stationary mill. The operator takes the readings by placing the sensor at selected points on the liner surface. The operator notes the thickness reading and the location on a graphical representation of the mill.
There are several problems with ultrasonic thickness gauging. Firstly, as mentioned previously, the mill must be decontaminated in order for the operator to enter the mill. Secondly, temperature alters sound velocity, and hence calibration is always needed to guarantee accurate readings. Thirdly, it is slow, as each point must be recorded manually. Fourthly, it is difficult to accurately assess liner wear due to the need to ensure that the sensor measurement tool is orthogonal to the mill shell, and the practical difficulty in achieving this.
Taking crushers as another example, before the ore passes to the mills it first passes through one or more crushers. Different types of crushers are used to break large solid materials into smaller pieces for further processing. For example, there exists jaw crushers, gyratory crushers, cone crushers and Cylindrical roll crushers such as High Pressure Grinding Rolls (HPGR). Crushers also have high wear surfaces which are protected by liners.
Gyratory crushers comprise a mantle which rotate in an eccentric relationship to the sides, known as concaves. These surfaces provide the crushing action and are protected by liners.
Over time, the mantle liner and the concave liners of the crusher wear and need replacing in order to maximise crusher efficiency and avoid crusher failure or damages to the crusher.
Mantle liners typically wear out quicker than the concave liners, particularly at the lower section. This can be corrected by adjusting the mantle position upwards during operation so as to maintain a steady or constant Closed Side Setting (CSS). If the CSS is not maintained, then undesired variable product sizes and/or production issues may result. Once the mantle can no longer be adjusted upward, the mantle is typically replaced by a larger size mantle liner so as to match the more worn liners on the concaves in order to maintain the CSS. Larger mantles continue to be installed in this fashion until the concaves need replacement.
Cone crushers function in a similar way, except that mantle and bowl liners are not necessarily relined at different times.
Usually several size mantles are used during the life cycle of one set of concaves. When the concave liners are new, an undersized mantle is used, when they are worn, a normal size mantle replaces the undersized version, and during the later stages of the concaves' life, an oversized mantle is installed. Depending on the site specific circumstances, less than or more than the three above mentioned sizes, or more than three sizes of mantles may be used in combination with one set of concaves, possibly by reusing mantle matched with the previous set of concaves as the next smaller size.
There are existing methods to check the condition of the mantle and concave liners in order to determine whether a crusher reline is necessary.
In most existing methods, there is a need for a person to access the crusher to take manual measurements during an inspection. However, a difficulty arises when the spider and mantle assembly is in place (typically the case for an inspection) as the person cannot access the crusher cavity. Therefore, it is not possible for the person to reach beyond the upper periphery section of the crusher in order to take manual measurements towards the bottom of the crusher, which is the most critical section to be analysed. In light of safety concerns, it is generally an unacceptable safety risk to lower a person in a harness into a crusher cavity when the mantle is still in place. Similarly, access to cone and jaw crushers is equally prohibitive because of their design and the surrounding infrastructure.
In the case of a typical fixed plant crusher, further difficulties arise when a person is required to access the crusher because of the safety requirement to completely clear the dump pocket (ROM bin) from any residual ore in order to get to the crusher itself. This is a major undertaking which is further complicated by the need for confined space isolation. This results in additional downtime, and hence loss in production and revenue.
Examples of existing crusher condition monitoring methods requiring physical access by a person to the crusher include:                Ball Drop Test        Visual or camera inspection        Tape measuring        Ultrasonic Thickness Gauging (UTG)        
These existing methods present difficulties as they are only possible to conduct when:                1) The ROM bin is completely cleared of ore;        2) The spider is removed;        3) The mantle/shaft assembly is removed;        4) Confined space isolation for the dump pocket is in place;        5) Confined space isolation for the crusher cavity is in place; and        6) Safety access systems such as steps, ladders, harnesses, scaffolding, and/or custom cavity platforms are available and deployed.        
Therefore, with the above existing methods, it is not possible to examine the crusher liners for wear at any time other than during a mantle reline, which is when the mantle/shaft is removed. As a result, it is not possible to examine the crusher liners for wear during an inspection shutdown, when any of items 1) to 6) listed above are not attained. This means that the only time when the mantle liners can be examined with the above existing methods is when the mantle is being relined anyway.
In addition, the above existing methods cannot provide reliable and accurate results, such as timing of reline. For example, the crusher could be relined more frequently than necessary, resulting in loss of production and extra costs.
Another area which experiences significant wear is in the transportation of material. Considering the mining industry in particular, ore at various stages of the processing process are transported through numerous means from the mine to its final destination. To assist in the transportation of the material large systems of conveyor belts are set up. Often the ore is required to travel from one conveyor belt to another. To ensure delivery of the ore between belts a transfer chute guides or redirects the ore to the next belt. This will often mean that the ore will impact on at least one of the walls of the transfer chute. In a similar vain to Crushers and Mills, the impact of the ore on these surfaces causes significant wear. To protect the surfaces from wear, the transfer chutes are lined with liners to protect the chute and to ensure no holes form in the transfer chute.
The design of a transfer chute is tailored to the particular application. As a result transfer chutes and the associated liners are many and varied in regards to their design. It is therefore necessary to monitor the liners on each transfer chute.
Currently the techniques used to monitor liner wear to evaluate liner change out are similar to those employed with mills and crushers. These techniques also face the same problems when monitoring transfer chutes. In particular, access to the internal surfaces of a transfer chute is generally unsafe, requires significant downtime of the conveyor system and has limitations with respect to confined space and working at height considerations.
Generally transfer chute are enclosed and have manholes at various stages to allow visual inspection. As the transfer chutes may be multi-storey there may be several manholes along the chute. These manholes do not allow for adequate surface measurement using known means. As a result it is necessary to construct scaffolding within the chute to allow for access and adequate measurement of the liners. This obviously requires significant time, and means that during the process that part of the conveyor system is inoperable.
Similar issues also apply to other material handling structures and numerous other industries and products. For instance transfer bins and hoppers, vessels. These all have the same inherent problem where it is very difficult to safely measure the wear of the various surfaces.
The following problems result from the inability to adequately monitor wear of surfaces, such as the wear of liners in mills, crushers and transfer chutes and bins:                Lack of awareness of liner wear rates and hence lack of control over change out schedules;        Lack of control over stock ordering of liners;        Lack of quantifiable control over the wear of different liner designs and hence inconclusive liner design comparisons and limitations in design optimization;        Lack of condition monitoring information on liner failures or wear hot spots in time to avoid failure or production issues;        Current condition monitoring methods are too cumbersome;        failure of liner plates can lead to excessive and unplanned downtimes to attend to repairs.        